Method, software and system for multi-path fail-over recovery in sequential storage systems

ABSTRACT

A method, software and system are disclosed for enabling multi-path error recovery of failed communicators with sequential storage device systems. In one embodiment, an information handling system (IHS) coupled to a sequential storage device via first and second communication paths is provided. Information exchanges between the IHS and the sequential storage device are monitored for communication path failure. In response to a failure event on a primary communication path, status of the halted information exchange is maintained by a host bus adapter and its supporting software on the IHS and in a fibre channel interface module of the sequential storage device. Status information regarding the halted information exchange is communicated to a fail-over host bus adapter of the IHS. The information exchange is completed on the fail-over communications path beginning from the point of failure such that data of the sequential information exchange is maintained in order.

TECHNICAL FIELD

The present invention relates generally to information handling systemsand, more particularly, to information handling system recovery aftercommunication path failures.

BACKGROUND

As the value and use of information continues to increase, individualsand businesses seek additional ways to process and store information.One option available to users is information handling systems. Aninformation handling system generally processes, compiles, stores,and/or communicates information or data for business, personal, or otherpurposes thereby allowing users to take advantage of the value of theinformation. Because technology and information handling needs andrequirements vary between different users or applications, informationhandling systems may also vary regarding what information is handled,how the information is handled, how much information is processed,stored, or communicated, and how quickly and efficiently the informationmay be processed, stored, or communicated. The variations in informationhandling systems allow for information handling systems to be general orconfigured for a specific user or specific use such as financialtransaction processing, airline reservations, enterprise data storage,or global communications. In addition, information handling systems mayinclude a variety of hardware and software components that may beconfigured to process, store, and communicate information and mayinclude one or more computer systems, data storage systems, andnetworking systems.

Host information handling system based multi-pathing software is usedgenerally to provide high availability to storage when multiple pathsexist through a fibre channel storage area network, for example. Suchsystems are commonly available for disk-based direct access devices.When a path to storage fails, the multi-path driver generally reroutesinput/output (I/O) operations to the storage system through an availableredundant or fail-over path. Since the device in this instance is directaccess, the multi-path driver is generally not concerned about thestatus of any I/O operations that are interrupted as a result of acommunication path failure. As a result, the multi-path driver willgenerally retry interrupted information exchanges assuming they werenever completed.

In the case of sequential storage devices, e.g., tape drives, however,this mechanism of multi-path fail-over error recovery is insufficient.For example, in a sequential storage environment, if data was written tomedia and the communication path failed while an operation status wasbeing returned, an attempt to retry the operation through the redundantpath may cause data to be written twice, resulting in inconsistent dataon the media. Further, in tape backup fibre channel environments,generally, there is no technology capable of rerouting error recoveryoperations for sequential devices from a failed primary path to asecondary or fail-over path. Current fibre channel recovery standardsgenerally only define link error recovery procedures on the same path asan original information exchange.

SUMMARY

In accordance with teachings of the present disclosure, a method isdescribed for recovering from a failure event on a communication pathbetween an information handling system and a sequential storage device.The method preferably includes monitoring the communication path duringan information exchange for a failure event. The method preferably alsoincludes marking, in response to detection of a failure event, a pointin the information exchange at which the failure event occurred. Inaddition, the method preferably includes initiating a continuation ofthe information exchange from the point of failure on a fail-overcommunication path between the information handling system and thesequential storage device.

Also in accordance with teachings of the present disclosure, softwarefor completing a transaction between a sequential storage device and ahost information handling system after a failure event on acommunication path between the sequential storage device and the hostinformation handling system is provided. According to teachings of thepresent disclosure, the software is preferably embodied incomputer-readable media and when executed, operable to detect a failureevent on the communication path. The software is preferably furtheroperable to retain information concerning at least one open exchangebeing communicated on the communication path and to retrieve an exchangestatus indicating a point in the exchange at which the failure eventoccurred. Further, the software is also preferably operable to continuecommunication of the exchange based on the exchange status on afail-over path between the host information handling system and thesequential storage device.

Further in accordance with teachings of the present disclosure, aninformation handling system including at least one processor, memoryoperably coupled to the processor and at least one communication deviceoperably coupled to the processor and the memory is disclosed. Thecommunication device is preferably operable to communicate data on atleast one communication path. In addition, the information handlingsystem preferably also includes a program of instructions storable inthe memory and executable by the processor. The program of instructionsis preferably operable to mark a point of failure in an informationexchange with a sequential storage device in response to a communicationpath failure. The program of instructions is preferably further operableto facilitate communication of the information exchange with thesequential storage device from the point of failure on a fail-overcommunication path.

In a first aspect, teachings of the present disclosure solve the problemof multi-path fail-over in sequential storage device environments byproviding a mechanism through which an interrupted information exchangeor sequence can be recovered from the point of failure using a fail-overor redundant communication path.

In a second aspect, teachings of the present disclosure minimize oreliminate inconsistent data written to sequential storage devices inresponse to attempts to recover from communication path failure events.

In a third aspect, the multi-path fail-over teachings of the presentdisclosure may be implemented in a manner that makes the fail-overprotection transparent to a host based tape backup software applicationoriginating communications.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 is block diagram illustrating one embodiment of a fibre channelsequential storage system and connected host information handling systemincorporating teachings of the present disclosure;

FIG. 2 is a flow diagram illustrating one embodiment of a method forimplementing multi-path fail-over error recovery in sequential storagesystems incorporating teachings of the present disclosure; and

FIG. 3 is a representation of one embodiment of a fibre channel extendedsequence retransmission request link service command incorporatingteachings of the present disclosure.

DETAILED DESCRIPTION

Preferred embodiments and their advantages are best understood byreference to FIGS. 1 through 3, wherein like numbers are used toindicate like and corresponding parts.

For purposes of this disclosure, an information handling system mayinclude any instrumentality or aggregate of instrumentalities operableto compute, classify, process, transmit, receive, retrieve, originate,switch, store, display, manifest, detect, record, reproduce, handle, orutilize any form of information, intelligence, or data for business,scientific, control, or other purposes. For example, an informationhandling system may be a personal computer, a network storage device, orany other suitable device and may vary in size, shape, performance,functionality, and price. The information handling system may includerandom access memory (RAM), one or more processing resources such as acentral processing unit (CPU) or hardware or software control logic,ROM, and/or other types of nonvolatile memory. Additional components ofthe information handling system may include one or more disk drives, oneor more network ports for communicating with external devices as well asvarious input and output (I/O) devices, such as a keyboard, a mouse, anda video display. The information handling system may also include one ormore buses operable to transmit communications between the varioushardware components.

Referring first to FIG. 1, a block diagram illustrating one embodimentof a multi-path information handling system and sequential storagedevice configuration is shown. According to teachings of the presentdisclosure, system 10 is preferably operable to overcome problemsassociated with communication path failure events during sequentialstorage device communications, write, read, advance, rewind, as well asother operations. In a preferred embodiment, teachings of the presentdisclosure solve problems associated with communication path failuresduring communications with a sequential storage device by providing amechanism through which an interrupted information exchange or sequencemay be recovered from its point of failure using redundant or fail-overcommunication paths.

As illustrated in FIG. 1, system 10 preferably includes informationhandling system 12 and at least one sequential storage device 14. In oneembodiment, information handling system 12 may be coupled to sequentialstorage device 14 via primary communication path 16 and at least oneredundant, secondary or fail-over communication path 18. The technologyon which communication paths 16 and 18 are based is SCSI (small computersystems interface) over fibre channel, fibre channel or any protocolthat transmits fibre channel. While the present disclosure makesreference to fibre channel communications, teachings of the presentdisclosure may be utilized with other technologies in existence andtechnologies currently in development.

Information handling system 12 preferably includes memory 20. Memory 20is preferably operable to store one or more instructions for executionin processor 22, as well as to store one or more aspects of data orinformation that can be utilized by information handling system 12.Processor 22 is preferably coupled to memory 20. In a preferredembodiment, processor 22 is preferably operable to communicateinformation or data maintained in memory 20 as well as to execute one ormore instructions maintained by memory 20 or elsewhere in informationhandling system 12, such as in one or more hard disk drive devices (notexpressly shown) or sequential storage device 14.

Also preferably included in information handling system 12, operablyassociated with memory 20 and processor 22, is sequential storageapplication 24. Sequential storage application 24 may be generallydefined as a program of instructions designed to assist the performanceof tasks related to management and manipulation of sequential storagedevice 14.

In addition to sequential storage application 24, information handlingsystem 12 preferably also includes sequential storage driver 26 operablyassociated with processor 22 and memory 20. Sequential storage driver 26may be generally defined as a program of instructions or hardware deviceoperable to control or regulate sequential storage device 14. Ingeneral, sequential storage driver 26 preferably handles specificfeatures of sequential storage device 14, freeing the operating systemrunning on information handling system 12 from the burden of having tounderstand and support the needs of sequential storage device 14.

SCSI (small computer systems interface) driver 28 is also preferablyincluded in information handling system 12, operably associated withmemory 20 and processor 22. In one embodiment of the present disclosure,communication paths 16 and 18 may be implemented using SCSI over fibrechannel. SCSI driver 28 may be employed to regulate one or more aspectsof SCSI communications over communication paths 16 and 18 as well as toperform other tasks in association with sequential storage device 14 orother components operably coupled to information handling system 12.

Also preferably coupled to memory 20 and processor 22 is support driver30. In one embodiment of teachings of the present disclosure, supportdriver 30 preferably facilitates one or more aspects of the multi-patherror recovery procedure for sequential storage systems as disclosedherein. Support driver 30 is preferably tightly coupled to HBA drivers40 and/or 42 or may be integrated into HBA drivers 40 and/or 42.Additional detail regarding the operation of support driver 30 withrespect to multi-path error recovery in sequential storage devicecommunications is discussed in greater detail below.

Communication devices 32 and 34 are also preferably included ininformation handling system 12 and operably coupled to memory 20 andprocessor 22. In one embodiment, communication devices 32 and 34preferably include host bus adapters (HBA) 36 and 38 and one or moreassociated HBA drivers 40 and 42, respectively. In one embodiment ofinformation handling system 12, HBA 36 and 38 may generally be definedas devices, typically in the form of an expansion card, for connecting aperipheral, e.g., sequential storage device 14, to information handlingsystem 12. As mentioned above, host bus adapters 36 and 38 may employfibre channel, SCSI, SCSI over fibre channel, as well as othercommunication protocols. Similar to sequential storage driver 26 andSCSI driver 28, HBA driver 40 and/or 42 may generally be defined as ahardware device and/or program of instructions that controls orregulates HBA 36 and 38, respectively. If a driver is implemented insoftware, the software driver may be generally defined as a devicespecific control program enabling an information handling system to workwith another information handling system, e.g., sequential storagedevice 14.

As illustrated in FIG. 1, sequential storage device 14 preferablyincludes first and second fibre channel ports 44 and 46, respectively.Sequential storage device 14 may also include ports in addition to fibrechannel ports 44 and 46, in alternate embodiments. As shown in FIG. 1,communication paths 16 and 18 connect information handling system 12 tosequential storage device 14 via connections between HBA 36 and fibrechannel port 44 as well as between HBA 38 and fibre channel port 46.

Sequential storage device 14 preferably also includes fibre channelinterface module 48. In one aspect, fibre channel interface module 48 ispreferably operable to receive communications from information handlingsystem 12 via communication path 16 and/or 18 such that informationhandling system 12 may communicate with medium changer 50 as well assequential drives 52, 54 and 56. In addition, as is described in greaterdetail below, fibre channel interface module 48 preferably cooperateswith support driver 30 as well as HBA 36 and/or 38 to effect multi-pathfail-over error recovery.

Referring now to FIG. 2, a flow diagram illustrating one embodiment of amethod for implementing multi-path fail-over error recovery insequential storage system is shown. In one aspect, teachings of thepresent disclosure describe an enhanced method of error recoveryutilizing a fail-over path to recover interrupted information exchangesfrom the point of failure between an information handling system and asequential storage device.

In the operation of method 70, if communication path 16 fails during aninformation exchange between information handling system 12 andsequential storage device 14, software and/or firmware on HBA 36 and/oron fibre channel interface module 48 of sequential storage device 14will preferably detect the error condition. When the error is detected,HBA driver 40, support driver 30 and fibre channel interface module 48of sequential storage device 14 preferably retain, mark or otherwisenote the state or point of failure of all open exchanges betweeninformation handling system 12 and sequential storage device 14 as wellas information about one or more logged-in devices, to permit latererror recovery. To protect against failed communications oncommunication path 16 due to failure of HBA 36, HBA driver 40 andsupport driver 30 is preferably operable to maintain awareness of eachpending information exchange being communicated thereon.

In an effort to effect error recovery procedures, the support driver 30will preferably propagate information about open exchanges at the pointof failure to HBA 42 on fail-over or redundant communication path 18. Ina preferred embodiment, the information propagated by support driver 30regarding open information exchanges preferably includes informationregarding an originator exchange identifier (OX_ID), a receiver exchangeidentifier (RX_ID) and a port identifier (ID) of the initiator. Oncecommunicated to sequential storage device 14, the originator exchange ID(OX_ID), receiver exchange ID (RX_ID) and port ID of the initiator maybe used by sequential storage device 14 to uniquely identify aninterrupted information exchange. In addition to passing informationassociated with the halted or interrupted information exchanges, HBAdriver 40 and support driver 30 preferably also pass a pointer to a databuffer containing the information to be communicated in the halted orinterrupted information exchange.

With the information concerning the open or halted information exchangesavailable, the error recovery process preferably continues with theinformation exchange originator issuing a read exchange concise (REC)extended link service command containing the originator exchange ID(OX_ID), the receiver exchange ID (RX_ID) and the port ID of theinitiator of the halted information exchange. Upon receipt of the RECextended length service command, sequential storage device 14 willpreferably retrieve from one or more fibre channel exchange buffersmaintained thereon the information exchange status based on the contentsof the REC extended length service command. In a preferred embodiment,sequential storage device 14 will preferably respond to the REC extendedlength service command with information retrieved from its buffersindicating the status as it pertains to sequential storage device 14 ofan associated halted or interrupted information exchange.

Upon receipt of the response from sequential storage device 14indicating its recorded, marked or otherwise noted status of aninterrupted or halted information exchange, HBA 38, via fail-over orredundant communications path 18, preferably issues an extended lengthservice command to begin the recovery process. In a preferredembodiment, the extended length service command is an extended sequenceretransmission request (ESRR). ESRR is one embodiment of a FibreChannel-4 link service command based on the sequence retransmissionrequest (SRR) Fibre Channel-4 link service request defined in the SCSIover fibre channel protocol.

Referring specifically now to method 70 of FIG. 2, upon initiation at72, method 70 preferably proceeds to 74. At 74, method 70 preferablyprovides for the determination as to whether an I/O (input/output)transaction or information exchange is pending on a primary HBA ofinformation handling system 12, such as host bus adapter 36. If an I/Otransaction or information exchange is not pending at 74, method 70preferably loops and awaits detection of a pending I/O transaction orinformation exchange. Alternatively, if a pending I/O transaction orinformation exchange is detected at 74, method 70 preferably proceeds to76.

In one embodiment, operations performed prior to the operationsperformed at 76 of method 70 may include determining whether primarycommunications path, such as communication path 16, is operable. In oneembodiment, determining whether a communication path is operable mayinclude, but is not limited to, determining whether a host bus adapterassociated with the primary communication path is operable as well asdetermining whether the communication path itself communicativelycouples information handling system 12 to sequential storage device 14,for example.

At 76, the pending I/O transaction information exchange detected at 74is preferably initiated on the primary host bus adapter via the primarycommunication path. In one embodiment, initiation of an informationexchange or I/O transaction between information handling system 12 andsequential storage device 14 may include the transmission of a requestfrom information handling system 12 to sequential storage device 14 forsequential storage device 14 to identify its receiver exchange ID(RX_ID). Upon return of the sequential storage device 14 receiverexchange ID (RX_ID), information handling system 12 may initiate aninformation exchange with sequential storage device 14.

In conjunction with initiating an information exchange or I/Otransaction on the primary host bus adapter and communication path ofsystem 10, method 70 preferably provides for substantially continuesmonitoring of at least the primary communication path, such ascommunication path 16, for a failure event. In one embodiment, HBAdriver 40 may monitor one or more aspects of HBA 36 as well as one ormore aspects of communication path 16 for one or more failure eventsindicative of an inability to communicate between information handlingsystem 12 and sequential storage device 14 via host bus adapter 36and/or communication path 16. If at 78 no failure in the link orcommunication path is detected, method 70 preferably proceeds to 80where a determination may be made as to whether the pending or currentinformation exchange has been completed. Determination as to whetherpending or current information exchange has been completed may include,but is not limited to, determining whether an acknowledgment has beenreceived from sequential storage device 14 indicating that sequentialstorage device 14 has received the last portion of the informationexchange or an indication that all data to be communicated has beencommunicated.

If at 80 it is determined that the pending or current informationexchange has not completed, method 70 preferably proceeds to 82 wherethe information exchange is preferably continued. In conjunction withcontinuing the information exchange at 82, method 70 preferably providesfor continued monitoring of the primary communication path and host busadapter facilitating the information exchange between informationhandling system 12 and sequential storage device 14. In a preferredembodiment, the communication link(s) of system 10 may be monitored forfailure without interruption to an open information exchange,eliminating a need for the affirmative operations preferably performedat 80 and 82. Alternatively, if at 80 it is determined that theinformation exchange has been completed, method 70 preferably returns to74 where the next I/O transaction or information exchange may beawaited.

If at 78, a link or communication path failure is detected during aninformation exchange, method 70 preferably proceeds to 84. At 84,according to teachings of the present disclosure, HBA driver 40 andsupport driver 30 are preferably configured to retain informationconcerning the state of all open information exchanges betweeninformation handling system 12 and sequential storage device 14. Inaddition, fibre channel interface module 48 of sequential storage device14 is preferably also configured to retain or mark informationassociated with the state of all open information exchanges associatedtherewith in one or more buffers preferably included on sequentialstorage device 14. In addition to retaining information associated withthe state of all open exchanges of information handling system 12 andsequential storage device 14, information concerning one or morelogged-in devices or devices communicatively coupled to informationhandling system 12 or sequential storage device 14 may also be stored byHBA driver 40, support driver 30 and/or fibre channel interface module48, respectively.

Following the marking or retention of information associated with one ormore open information exchanges between information handling system 12and sequential storage device 14 at 84, method 70 preferably proceeds to86. At 86, support driver 30 preferably communicates the information ithas retained regarding the halted or open information exchanges to HBAdriver 42 associated with HBA 38 which is preferably operably coupled tofail-over or redundant communication path 18.

In one embodiment, the information communicated by support driver 30from HBA driver 40 to HBA driver 42 includes, but is not limited to, anoriginator exchange ID (OX_ID), a receiver exchange ID (RX_ID) and theport ID of the initiator, e.g., a twenty-four (24) bit fibre channel ID.In the fibre channel protocol, as well as in the SCSI over fibre channelprotocol, information exchange target device, such as sequential storagedevice 14 in a situation where information handling system 12 isattempting to write data to one or more drives 52, 54 and/or 56 ofsequential storage device 14, may use the originator exchange ID(OX_ID), receiver exchange ID (RX_ID) and port ID of the initiator touniquely identify a halted or open exchange. In addition tocommunicating the originator exchange ID (OX_ID), receiver exchange ID(RX_ID) and port ID of the initiator, support driver 30 preferably alsocommunicates a pointer to a data buffer containing information that wasbeing propagated in the halted information exchange.

Following communication of the originator exchange ID (OX_ID), receiverexchange ID (RX_ID) and port ID of the initiator, method 70 preferablyproceeds to 88. At 88, the fail-over host bus adapter, such as HBA 38,cooperating with HBA driver 42 and support driver 30 preferably issues aread exchange concise (REC) extended link service command to the targetdevice of an information exchange, such as sequential storage device 14,requesting the target device read its marked or retained status of thehalted or open information exchange. In a preferred embodiment, the RECextended link service command preferably includes the originatorexchange ID (OX_ID), receiver exchange ID (RX_ID) and port ID of theinitiator associated with the halted or interrupted information exchangedesired to be recovered and completed. Upon receipt of the REC extendedlink service command from information handling system 12, sequentialstorage device 14, specifically fibre channel interface module 48 in apreferred embodiment, will preferably retrieve from one or more buffersincluded thereon its marked or retained status of the halted informationexchange based on the contents of the REC extended link service commandcontents associated with the halted or interrupted information exchange.After retrieving the marked or retained status information concerningthe interrupted or halted information exchange, the target device, suchas sequential storage device 14, preferably responds to the REC extendedlink service command with data indicating fibre channel interface module48 buffer contents associated with a sequential storage device 14recorded status of the interrupted or halted information exchange.

Upon receipt of a response from sequential storage device 14 to the RECextended link service command communicated by information handlingsystem 12, method 70 preferably proceeds to 90. At 90, informationhandling system 12 preferably issues an extended sequence retransmissionrequest (ESRR) extended link service command to initiate recoveredcommunication of the halted or interrupted information exchange on thefail-over communication path using the fail-over host bus adapterpreferably included on information handling system 12. In general, anESRR extended link service command effectively restarts a halted orinterrupted communication exchange from the point of failure noted,marked and/or retained by HBA driver 40 and/or fibre channel interfacemodule 48 in response to detection of a communication failure betweeninformation handling system 12 and sequential storage device 14.

Following the issuance of an ESRR extended link service command at 90,method 70 preferably proceeds to 92 where the information remaining tobe communicated in the halted or interrupted information exchange ispreferably transmitted on the fail-over or redundant communication pathfrom the detected point of failure to completion. As with the continuedinformation exchange communications at 80, following initiation ofretransmission of remaining portions of a halted or interruptedinformation exchange at 92, method 70 preferably provides for continuedmonitoring of the fail-over or redundant communication path preferablyincluded between information handling system 12 and sequential storagedevice 14.

Although not explicitly shown, one or more additional operations may beincluded in method 70 to address additional aspects of communicationpath failures between information handling system 12 and sequentialstorage device 14. For example, provision may be made for the exhaustionof redundant or additional fail-over communication paths betweeninformation handling system 12 and sequential storage device 14 suchthat once each communication path between information handling system 12and sequential storage device 14 has been determined to have failedcommunications, method 70 may provide for the retention of informationassociated with each halted or interrupted information exchange andprovision of error recovery options similar to those above upon thedetection of re-established communications between information handlingsystem 12 and sequential data storage device 14.

Referring now to FIG. 3, one embodiment of an extended sequenceretransmission request (ESRR) extended link service command is showngenerally at 100. As indicated in FIG. 3, one embodiment of an ESRRextended link service command includes five thirty-two-bit (32-bit)words. As indicated at 102, bits zero through thirty-one (31) of wordzero (0) preferably include a command identifier. The command identifierindicates that this command is an ESRR. In a preferred embodiment,substantially all commands executable between information handlingsystem 12 and sequential data storage device 14 via the fibre channelprotocol, SCSI over fibre channel protocol, as well as other protocolsmay be effected.

In addition to command identifier 102, ESRR extended link servicecommand 100 preferably also includes, in word one (1), the originatorexchange ID (OX_ID) 104 and the receiver exchange ID (RX_ID) 106 at bitssixteen (16) through thirty-one (31) and zero (0) through fifteen (15),respectively. At bits zero (0) through thirty-one (31) of extended linkservice command word two (2), the ESRR extended link service commandword 100 preferably includes a sequence restart offset. In oneembodiment, the sequence restart offset indicates the point at which theinterrupted or halted information exchange should be restarted.Conceptually, sequence restart offset 108 may be generically defined asa pointer to the starting point for the recovery of communicationsbetween information handling system 12 and sequential data storagedevice 14 regarding the halted or interrupted information exchange. Atbits twenty-four (24) through thirty-one (31) of ESRR extended linkservice command word three (3), routing control information incorporatedin the fibre channel protocol, the SCSI protocol and/or the SCSI overfibre channel protocol may be included. The routing control filed is asdescribed in FC-FS and tells what phase of a fibre channel exchangeneeds to be recovered, e.g., data descriptor, command status, soliciteddata, etc. At 112, the port ID of the initiator is preferably includedat bits eight (8) through thirty-one (31) of ESRR extended link servicecommand 100 word four (4).

Although the disclosed embodiments have been described in detail, itshould be understood that various changes, substitutions and alterationscan be made to the embodiments without departing from their spirit andscope.

1. A method for recovering from a failure event on a communication pathbetween an information handling system and a sequential storage device,comprising: monitoring the communication path during an information dataexchange for a failure event; in response to detection of a failureevent, using an identifier to indicate a location in the informationdata exchange at which the failure event occurred; and initiating acontinuation of the information data exchange from the location offailure on a fail-over communication path between the informationhandling system and the sequential storage device.
 2. The method ofclaim 1, further comprising indicating the location of failure in a hostbus adapter of the information handling system.
 3. The method of claim1, further comprising indicating the location of failure in thesequential storage device.
 4. The method of claim 1, further comprisingcommunicating the location of failure to a fail over host bus adapter onthe information handling system using a support driver.
 5. The method ofclaim 1, wherein the identifier comprises at least one of an originatorexchange identifier, a receiver exchange identifier and a portidentifier.
 6. The method of claim 1, further comprising querying thesequential storage device by the information handling system foridentification of its indicating the location of failure.
 7. The methodof claim 6, further comprising initiating continuation of theinformation data exchange based on sequential storage device queryresults.
 8. The method of claim 1, further comprising passing a pointerto a buffer including contents of the information data exchange from ahost bus adapter associated with the failed communication path to a failover host bus adapter associated with a fail over communication path. 9.Software for completing a transaction between a sequential storagedevice and a host information handling system after a failure event on acommunication path between the sequential storage device and the hostinformation handling system, the software embodied in computer readablemedia and when executed operable to: detect a failure event on thecommunication path; retain information concerning at least one openexchange being communicated on the communication path; retrieve anexchange status using an identifier to indicate a location in theinformation data exchange at which the failure event occurred; andcontinue communication of the exchange based on the exchange status on afail over path between the host information handling system and thesequential storage device.
 10. The software of claim 9, further operableto query the sequential storage device for the exchange statusindicating the location in the information data exchange at which thefailure event occurred.
 11. The software of claim 9, further operableto: read open exchange information from a host bus adapter associatedwith the failed communication path; and communicate the open exchangeinformation to a host bus adapter associated with the fail overcommunication path.
 12. The software of claim 9, further operable tomonitor continued communication of the exchange for an acknowledgment ofexchange completion.
 13. The software of claim 9, further operable tobuffer data received in the exchange communication at the sequentialstorage device.
 14. The software of claim 9, further operable to retaininformation concerning at least one open exchange on the hostinformation handling system and the sequential storage device.
 15. Aninformation handling system, comprising: at least one processor; amemory operably coupled to the processor; at least one communicationdevice operably coupled to the processor and the memory, thecommunication device operable to communicate data on at least onecommunication path; and a program of instructions storable in the memoryand executable by the processor, the program of instructions operable touse an identifier to indicate a location of failure in an informationdata exchange with a sequential storage device in response to acommunication path failure and facilitate communication of theinformation data exchange with the sequential storage device from thelocation of failure on a fail over communication path.
 16. Theinformation handling system of claim 15, further comprising the programof instructions operable to respond to a query concerning theinformation data exchange location of failure.
 17. The informationhandling system of claim 15, further comprising the program ofinstructions operable to query the sequential storage device to identifythe information data exchange location of failure.
 18. The informationhandling system of claim 15, further comprising the program ofinstructions operable to communicate data concerning the informationdata exchange to communication hardware associated with the fail overcommunication path.
 19. The information handling system of claim 15,wherein the identifier includes at least one of an originator exchangeidentifier, a receiver exchange identifier and a port identifier. 20.The information handling system of claim 15, further comprising: a firsthost bus adapter operable to communicate with the sequential storagedevice along a first communication path; a second host bus adapteroperable to communicate with the sequential storage device along asecond communication path; and at least one host bus adapter operable toretain an exchange state for at least one open exchange beingcommunicated on an associated communication path.
 21. The informationhandling system of claim 15, further comprising: a fibre channelinterface module operable to receive at least one informationdata_exchange on a communication path; and the fibre channel interfacemodule operable to retain an exchange state for at least one openexchange communicated on the communication path.